OT-House Wiring

What I am planning on doing is wiring in an auxiliary electrical panel across from the main load center/panel. Went to Home Depot to get a sub-panel, but noticed that the 100-amp 12-position sub-panel cost $51 without any breakers. Right next door in the same aisle is a 100-amp 20-position load center/main panel with the 100-amp breaker and 6 20-amp breakers included for $60. These are both Square-D Homeline boxes. My logic tells me the 100-amp load center is the better deal money wise, safety wise, and roominess wise. Plan to gound this auxilaiary box with 2 5/8" ground rods and feed it with #2 copper in 2" PVC conduit (about a 35' run).

If anyone sees something here that may cause a problem with safety or something else, please reply.

Unlike at the Main Service Entrance panel the Neutral and Ground busses are SEPERATE AND ISOLATED. At the sub panel the panels metal case is bonded to the Ground Buss but NOT the Neutral buss, its isolated.

Therefore, if you run wires from a main 120/240 Single Phase Three Wire panel to a sub panel you would use FOUR WIRES. Two Hots (Black n Red) One Neutral (white grounded conductor) one bare or green ground.

Usually the sub panel is lugs only no main breaker cuz the feeders are protected by the breaker in the main panel that feeds the sub panel

John T retired Electrical Engineer

If the safety equipment ground buss was to mother earth ONLY and a hot wire got against the drills metal case, the earth is a high resistance path (depends on moisture n iron content etc etc) and a 20 amp breaker wouldnt trip buttttt tttt it only takes something like 50 milliamps through the old ticker to defibrilate it n you dieeeee eee cuz the breaker donT trip but the case is still hottttt

Out at the utility pole or pad mount transformer theres a transformer whose low voltage secondary winding has voltage between its 2 hot phases (240) and either phase and the center tapped Neutral (120). Current wants to flow via a conductor across/between those potential difference transformer terminals NOT from either to mother earth. The reason neutrals are tied to mother earth is so all have a common single zero voltage reference potential and earth is the best to use. The safety equipment ground buss and all those bare/green wires to an appliance metal case are there for fault current return so the breaker can trip and thats whyyyyy y its bonded to the Neutral at the panel cuz thats the place where current wants to flow NOT SO MUCH HIGH RESISTANCE EARTH.

Sooooo you carry seperate n isolated Neutrals (grounded conductor) n grounds (safety equipment grounding conductors) to the sub panels and DO NOT re bond them again (to prevent a situation where the right combinations of open neutrals n shorts may energize the ground buss circuit n you touch it n die) and theres no bonding of the equipment ground buss to mother earth cuz that dont do jack crap lol its the Neutral that gets bonded to mother earth at transformers n main panels for reasons above.

Hope this helps

PS just cuz Im an engineer dont necessarily mean I know know a dern thing more (probably less actually) then many other experienced electricians n others who answered, so go with their opinions also as Im long retired n very NEC rusty enginerr yet Im still knee deep in theory

John T

If the safety equipment ground buss was to mother earth ONLY and a hot wire got against the drills metal case, the earth is a high resistance path (depends on moisture n iron content etc etc) and a 20 amp breaker wouldnt trip buttttt tttt it only takes something like 50 milliamps through the old ticker to defibrilate it n you dieeeee eee cuz the breaker donT trip but the case is still hottttt

Out at the utility pole or pad mount transformer theres a transformer whose low voltage secondary winding has voltage between its 2 hot phases (240) and either phase and the center tapped Neutral (120). Current wants to flow via a conductor across/between those potential difference transformer terminals NOT from either to mother earth. The reason neutrals are tied to mother earth is so all have a common single zero voltage reference potential and earth is the best to use. The safety equipment ground buss and all those bare/green wires to an appliance metal case are there for fault current return so the breaker can trip and thats whyyyyy y its bonded to the Neutral at the panel cuz thats the place where current wants to flow NOT SO MUCH HIGH RESISTANCE EARTH.

Sooooo you carry seperate n isolated Neutrals (grounded conductor) n grounds (safety equipment grounding conductors) to the sub panels and DO NOT re bond them again (to prevent a situation where the right combinations of open neutrals n shorts may energize the ground buss circuit n you touch it n die) and theres no bonding of the equipment ground buss to mother earth cuz that dont do jack crap lol its the Neutral that gets bonded to mother earth at transformers n main panels for reasons above.

Hope this helps

PS just cuz Im an engineer dont necessarily mean I know know a dern thing more (probably less actually) then many other experienced electricians n others who answered, so go with their opinions also as Im long retired n very NEC rusty enginerr yet Im still knee deep in theory

John T

I have 350Amp service coming in at the meter (same price as 200A). The run is split at the meter box and goes inside to a 200 A load center and a sparate 200A stand alone main breaker. This load center feeds my basement and 1st floor. The stand alone breaker feeds another 200 Amp load center in the attic that serves the 2nd floor and attic.

Much more efficent when adding a new outlet in the attic.

There is a higher cost for the 400A meter box and the added cost for the stand alone breaker.

Something for you to consider,

Cliff (VA)

steveormary

Charles

You need to run a separate equipment grounding conductor (along with the hot and neutral wires) from the main panel to your sub-panel. It needs to be 8AWG copper or larger. You should NOT add any ground rods or tie the sub-panel to an external ground in any way (except through the equipment grounding conductor).

You need to isolate the ground from neutral at the sub-panel. Typically this involves removing a particular screw or screws that tie the panel case to the neutral bar, and adding a separate ground bar if one is not already there. The branch circuits that start at the subpanel need to have the neutral run to the neutral bar, and the ground run to the ground bar (unlike what you'll find in a typical main panel).

Your feeder (from the main to the sub) needs to be protected at the main panel by a suitable 2 pole breaker, regardless of any main breaker in the subpanel.

You can use the biggest, baddest panel you want for your sub-panel. The big-box pricing, as you've observed, has some interesting anomalies. A 200 amp, 42 circuit panel would be fine. Just make sure the connection lugs on the sub are listed for the size conductors you run -- sometimes a 100 amp feeder results in conductors too small to fit the lugs on a 200 amp panel.

PVC conduit, while allowed, is rarely suitable inside buildings. It isn't flexible enough to run through joists or studs, yet provides only questionable protection when run on the surface.

NM cable, SE cable, or flex conduit are better options for running through joists or studs. EMT is a better choice for running exposed. The 2 inch trade size you propose is needlessly large -- 1.5 inch or 1.25 inch appears to be adequate.

Building codes or not, you have a responsibility to future generations to make the wiring code compliant and safe. As I've gotten older, I've realized that none of us really "own" our possessions -- we just get to use them for a while until we die and the next guy takes them over.

Its possible to have the right/wrong combination of open conductors and/or shorts such that the equipment ground system (whats tied to metal cases of some tools n appliances) could become energized n shock n kill someone..... .

At the service entrance the Neutral (grounded conductor) is bonded to mother earth (zero potential reference) by made grounds such as driven into earth copper rods or other to earth grounds like metal water or gas pipes etc and the Neutral n Ground Busses are bonded together so the safety equipment ground buss (and its green or bare equipment grounding condustors) can serve as a low impedance current return path FOR FAULT CURRENT ONLY so the breaker will trip n save life and/or fires.

The earth grounding is for tying service Neutrals to a common zero potential earth grund reference while the bare/green safety equipment ground is for safety n fire prevention to provide a low impedance return current path to trip a circuit breaker in the event of a fault. Its for fault current ONLY while the Neutral (a grounded conductor) carries the normal non fault current to complete the circuit.

Hope this helps

John T retired Electrical Engineer

Only one ground spot per building.

If this were a seperate building, then never mind.

When I had my farm rewired, ran into an interesting deal. You are only allowed one power feed into a building. I had a building with 120v coming into a fuse box (ran one lightbulb & one plug). Same building housed the well controls, and had 240v into that corner. At the time of wiring back in the '70s this second feed was ok I guess, as it was dedicated to the well. Had to be re-mapped tho in this decade, one feed to the building.

--->Paul

[Quote]>Link "Why not connect the neutral and ground at other points in the system? Because if a neutral wire became disconnected (I've seen it happen), the return path for electric current could be along a ground wire. While that itself may not be a hazard, if that ground wire also became disconnected somewhere, parts of the ground system could be energized. That's not EVER supposed to happen.

The neutral wire is essentially a "low-risk" return path for the electric current in that branch of the system. All of the neutral wires all have the same electrical potential... nothing. At least, no potential compared to ground. There is, of course, 120 volts of potential difference between a neutral wire and any hot wire in the residential system.

If you touched the metal part of a live neutral wire you should not receive a shock. (But don't try it!) By tying the neutral to ground at one point, half of the conductors (in a typical 120 volt circuit) have no dangerous electrical potential. Of course, the hot wires are still dangerous." [End Quote]

From Ken: "Why are you using copper since its more money than aluminum ? "

I have some left over from a previous wiring project. 3 reels of approximately 75' each.

From David-OR: "Your feeder (from the main to the sub) needs to be protected at the main panel by a suitable 2 pole breaker, regardless of any main breaker in the subpanel."

Yup, noticed I didn't include that in my original after posting. Wish there was an edit feature on here. Putting a 70-amp breaker in the main to feed the "sub".

From David-OR: "Building codes or not, you have a responsibility to future generations to make the wiring code compliant and safe. As I've gotten older, I've realized that none of us really "own" our possessions -- we just get to use them for a while until we die and the next guy takes them over."

Well put and couldn't agree with you more. As long as I can afford it I usually will do overkill on any project I get involved with.

Still not sure why I wouldn't add the 2 ground rods to the new panel though. Sounds like extra protection to me. If I can do without them it would sure save a bunch of work and about $30. The rock to soil ratio here is about 50/50 at best. If anything the ratio would be tipped in favor of rock.

I am a little confused on your reasoning for not grounding the auxiliary/sub panel. It's my understanding that the new panel should have a seperate ground bar isolated from neutral. The ground bar will be tied back to the main panel via a #4 or #6 wire. I could understand there being a problem if one of the grounding connections were loose and not making good contact. If all were done properly then it would seem to me that I would have a much larger and better ground field. I am a believer in proper grounding after 35 years with GTE/Verizon. Also 4 years in the USN as an Electronics Tech. I'm not saying an electronics tech is an electrician, but I do have a working knowledge of electricty and it's eccentricities. I am always willing to learn though and thanks to all the repliers.

I wouldn"t use PVC conduit either. THW/THWN in EMT or NM cable.

Not knowing the numbers of the panelboard/load center it would be hard to say- but if one is a panelboard it is a much higher grade piece of equipment than a load center. There isn"t anything wrong with a loadcenter, has to do with AIC ratings, layout etc. Probably both are load centers as I don"t know of any Homeline that isn"t.